I inherited my in laws 50 gallon tank, and I know what all the rest of the fish are but this one velvety black big eyed fish. They suspect it is a catfish of some sort, and picked it up from a free tank at our local fish store. He is about 6 inches long, and spends most of his time trying to get under everything in the tank including the other fish. I want to make a more comfortable home for him, but don't know what he is or what he needs.
I apologize for the horrible pictures, he and the pleco wouldn't cooperate very much.

(Ignore Goliath's head in the picture.)
Any help in sending me in the right direction would be very much appreciated.